Re: Register numbers on hppa64

["John David Anglin" <dave@hiauly1.hia.nrc.ca>]

> > If we change the register use in .dwarf_frame, then we are breaking
> > compatibility with previously compiled code.  This isn't a big deal
> > under HP-UX (dwarf debugging was totally broken on hppa64 until a
> > recent assembler fix).  However, there is a fair bit of installed
> > code running linux.  Thus, I would say not change the status quo
> > if the above confusion can be handled.  The actual numbers used for
> > the FP registers are obscure and I doubt many people actually care
> > what they are.  It's only people maintaining the dwarf code that
> > are likely to get confused.  If readelf produced a text rather than
> > numeric representation, then the problem would largely go away.
> 
> If I understand Mark correctly, the suggestion would change the 
> numbering used for dwarf cfi/eh, but not the register numbers emitted 
> for .debug_info, right?

It would change the numbering in .debug_frame but not .eh_frame
if I understand correctly.  We could change to dbx numbers everwhere
but that would have a much more significant on the ABI and make the
frame tables for unwinding much larger.  The positive side is that
it would allow recording more information in the frame state if
required.

> FWIW currently on hppa-linux, gdb does not use dwarf cfi for frame 
> unwinding. It's on my list of things to do, but if something need 
> changing in gcc for whatever reason, now is a good time to do it as far 
> as I'm concerned.

That certainly would provide a test as to whether we are providing
the correct call frame information in all cases.  I guess there may
be problems with unwinding through signal frames with really old
kernels.

I'm still not convinced that the numbers in gcc need changing.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)